Polymer compositions are used in the formulation of various coating compositions such as floor finishes, for example. Commercially available floor finish compositions typically are aqueous emulsion based polymer compositions comprising one or more organic solvents, plasticizers, coating aids, antifoaming agents, polymer emulsions, waxes and the like. These compositions typically comprise a relatively low solids content (e.g., about 15-35%). The polymer composition is applied to a floor surface and then allowed to dry in air, normally at ambient temperature and humidity to form a film that serves as a protective barrier against soil deposited on the floor by pedestrian traffic, for example.
Although many of the commercially available floor finishes have performed well and have experienced at least some commercial success, the available finishes have been less than completely satisfactory for several reasons. For example, when applying conventional floor finish compositions to the surface of a floor, several coating applications are typically required to obtain a finish with a suitable appearance. Each successive application of the composition must be dried before additional coatings are applied and/or before pedestrian traffic is allowed across the treated floor. The compositions are normally dried at ambient temperature and humidity in air, so that the drying time depends upon the air flow over the floor as well as the relative humidity of the air. Conventional floor finishes will soften when exposed to water for short periods or when exposed to strong chemical cleaners during a scrubbing operation, for example. Moreover, such finishes require almost daily maintenance (e.g., buffing) to provide a sustained and desirable appearance.
In light of the foregoing, it is desirable to provide a floor finish composition that can be applied in a single application and immediately dried and hardened in air to provide a durable, low maintenance, water-resistant, chemically resistant finish that does not require labor intensive (e.g., daily) maintenance to provide a sustained and desirable appearance. It would also be desirable to provide such a durable, low maintenance, water-resistant, chemically resistant finish in a form that can readily be removed from the surface to which it is applied, such as from flooring comprising conventional vinyl floor tiles, for example.
It is known that irradiation of ethylenically unsaturated compounds in the presence of a photoinitiator induces photopolymerization. As used herein, "photoinitiator" refers to any substance or combination of substances that interact with light to generate free radicals capable of inducing free radical polymerization. Photochemical or photo initiated free radical polymerizations occur when radicals are produced by ultraviolet ("UV") and/or visible light irradiation of a free radical polymerizable reaction system. Energy absorption by one or more compounds in the system results in the formation of excited species, followed by either subsequent decomposition of the excited species into radicals or interaction of the excited species with a second compound to form radicals derived from both the initially excited compound and from the second compound. The exact mechanism for photoinitiation is not always clear and may involve either or both of the aforementioned pathways.
Photochemical polymerization has been applied in the formation of decorative and/or protective coatings and inks for metal, paper, wood and plastics as well as in photolithography for producing integrated and printed circuits and in curing dental materials. Many of the known applications involve a combination of photopolymerization and crosslinking with the crosslinking typically achieved by the used of ethylenically polyunsaturated monomers. Acrylate based systems are common as well as those based on unsaturated polyester and styrene.
Additionally, UV curable protective finishes have been applied to vinyl "no wax" flooring during the sheet manufacturing process to provide gloss as well as abrasion resistance. These protective finishes generally cannot be easily stripped from the flooring to which they are applied using conventional stripping methods (e.g., by the application of a chemical stripping composition with a stripping pad or brush). Furthermore, the curing of these finishes is typically carried out using high intensity light. The lamps have high power requirements, large power supplies and generally require ducted venting to remove ozone. Often, these finishes are cured in an inert atmosphere to overcome the deleterious effects of oxygen on the curing process. Because of the above noted power requirements and the like, the use of UV curable polymeric systems in the treatment of flooring has generally been limited to factory scale processes where the expense and additional burdens associated with these systems is more easily justified.
Other problems have been noted in the formulation of UV curable systems for pre-existing flooring (e.g., previously installed in a building). In the application of any type of finish to an existing floor, it is generally preferred that the hardened floor finish not alter the color of the floor. To accomplish this goal, the finish should be transparent and substantially free of observable color. This goal is especially desired in the maintenance of floors composed of white floor tiles where an observable color in the hardened finish will more noticeably produce an observable discoloration in the floor. Additionally, to make a floor finish composition acceptable for application in the field, the applied floor finish should also have low odor prior to curing.
It is known, for example, that certain resins containing functional polymerizable vinyl groups, such as acrylate or vinyl ether/maleate containing an amine or a thiol, are polymerizable in air by free radical polymerization when exposed to UV or visible light in the presence of a photoinitiator. Although tough, abrasion resistant coatings can be provided using such resins, the resulting coatings are typically colored, with colors ranging from yellow to dark orange or have an objectionable odor prior to curing. Consequently, these resins are considered unsuitable for use as floor finishes.
As mentioned, atmospheric oxygen is known to inhibit photoinitiated polymerization reactions, resulting in little or no cure on the surface of the coating or providing a coating with poor surface properties. Various processing techniques have been proposed to eliminate the effects of oxygen from the reacting resin. One approach is to isolate the coating in a chamber and purge the chamber with an inert gas (e.g., nitrogen) so that the polymerization reaction proceeds in an environment substantially free of oxygen. Another approach is to initiate the polymerization reaction using intense UV radiation in conjunction with the high levels of photoinitiator in the uncured resin. Neither of these proposed techniques are practical in providing a floor finish system for use on previously installed flooring. Although smaller, lightweight, inexpensive, low intensity light sources capable of operating on batteries or on 110 volt, 15 amp circuitry would be preferred, known UV curable polymer systems have experienced slower rates of cure and higher cure inhibition when low intensity light has been used.
A long felt and unsolved need exists for a coatable composition suitable for use as a floor finish that can easily be applied to a substrate, such as a previously installed floor, and hardened in air upon exposure to low intensity radiation such as ultraviolet light, for example. It is desirable to provide such a coatable composition, preferably without objectionable odor, in a form that may be easily applied to a floor and subsequently hardened to provide a protective coating substantially free of observable color. It is also desirable to provide the foregoing protective coatings in a form that allows them to be removed from the floor (e.g., by a suitable chemical stripper), as desired.